Yahoo mail dropping 2 digits on password

On my iPhone 3 I have a Yahoo mail account through AT&T (sbcglobal.net). This morning it won't send or retrieve email from this account, saying the email address, or password is incorrect. When I go into email settings, the password has dropped two digits. So I have gone back several time to type in the correct password. After it validates the account, the same two digit are dropped (last two). Help!